In the fuel supply system for a fuel injected internal combustion engine present in many modem automotive vehicles, a fuel pump driven by an electric motor continuously supplies liquid fuel to the fuel injector(s) of the engine at a substantially constant flow rate which is always more than sufficient to supply the maximum possible fuel demand of the engine. Thus, under most engine operating conditions and particularly when the engine is merely idling, the fuel pump produces a significant amount of excess fuel that must be returned to the fuel tank from which the fuel pump originally drew the fuel.
Some fuel systems supply the entire fuel output of the pump to the engine and return the excess fuel from the engine to the fuel tank. Other fuel systems divert or bypass the excess fuel before it is delivered to the engine. Such a fuel system is commonly referred to as a "no return" or "returnless" type of system because it neither requires nor has a fuel return line extending from the fuel rail of the engine itself and back to the fuel tank. One prior returnless fuel system is disclosed in U.S. Pat. No. 5,975,061 issued on Nov. 2, 1999 to Briggs et al. In this system, the fuel pump continuously operates at maximum fuel output capacity, and the excess fuel is diverted from the engine and returned to the tank by a bypass fuel pressure regulator which maintains a substantially constant pressure of fuel supplied to the engine even though the fuel flow rate varies.
Another returnless fuel system is disclosed in U.S. Pat. No. 5,265,644 in which changes in the instantaneous pressure of the fuel supplied to the engine actuate a switch to change the speed of the electric motor to vary the fuel output of the pump through appropriate pulse width modulation circuitry which changes the electric power applied to the pump motor.
While these systems do attempt to deliver an amount of fuel to the engine which better matches the actual fuel demand of the engine, they are often inaccurate and untimely, especially when there is a sudden and significant rise or fall in the fuel demand of the engine, and sometimes momentarily result in insufficient fuel being supplied to the engine. Thus, there is a present need in the art for an apparatus which better and more rapidly and timely matches the actual fuel demand of the engine.